Touchscreen displays are able to detect a person's touch within the active or display area, such as detecting whether a finger is present pressing a fixed-image touchscreen button or detecting the presence and position of a finger on a larger touchscreen display. Some touchscreens can also detect the presence of elements other than a finger, such as a stylus used to generate a digital signature, select objects, or perform other functions on a touchscreen display.
Touchscreens are often used as interfaces on electronic devices, appliances, and other such electronic systems because the display behind the touchscreen can be easily adapted to provide instruction to the user and to receive various types of input, thereby providing an intuitive interface that requires very little user training to use effectively. Inexpensive and efficient touchscreen technologies enable incorporation of touchscreens into inexpensive commercial devices, but these inexpensive technologies should also desirably be durable and have relatively high immunity to noise, moisture or dirt, or other unintended operation to ensure reliability and longevity of the touchscreen assembly. These desirable attributes also largely apply to other input devices such as trackpads and pen entry tablets.
Use of a touchscreen as part of a display also allows an electronic device to change the display image, presenting different buttons, images, or other regions that can be selected, manipulated, or actuated by touch. Touchscreens can therefore provide an effective user interface for cell phones, GPS devices, personal digital assistants (PDAs), computers, ATM machines, and other such devices.
Touchscreens use various technologies to sense touch from a finger or stylus, such as resistive, capacitive, infrared, and acoustic sensors. Resistive sensors rely on touch to cause two resistive elements overlaying the display to contact one another completing a resistive circuit, while capacitive sensors rely on the capacitance of a finger changing the capacitance detected by an array of elements overlaying the display device. Infrared and acoustic touchscreens similarly rely on a finger or stylus to interrupt infrared or acoustic waves across the screen, indicating the presence and position of a touch.
Minimizing process steps to produce the touchscreen overlay and minimizing external wiring connections further reduce the cost of producing such a touchscreen display, and makes interfacing the display with electronic control circuitry more straightforward and reliable. Reducing wiring density and number also reduces the number of pins required on a controller chip used to drive the electrode array, which can result in significant space and cost savings. Additionally, it is desirable to reduce the layer count of the touchscreen assembly to reduce cost, reduce light absorption or other optical effects (in applications where this is important), and to increase production yields. Various methods have been proposed and implemented in prior designs to simplify electrode wiring requirements, but often at the expense of other design compromises such as reduced touch resolution or added complexity or cost in other areas.
Capacitive and resistive touchscreens often use transparent conductors such as indium tin oxide (ITO) or transparent conductive polymers to form an array over the display image, so that the display image can be seen through the conductive elements used to sense touch. The size, shape, and pattern of circuitry have an effect on the accuracy of the touchscreen, as well as on the visibility of the circuitry overlaying the display. Although a single layer of most suitable conductive elements is difficult to see when overlaying a display, multiple layers can be easier to see, and circuitry patterns that align closely with patterns on the display can form visible interference or moiré patterns.
Further, more complex patterns of touchscreen elements can require more complex routing of lines connecting the elements to external circuitry used to sense touch, such as external circuitry that drives various touchscreen elements and that detects capacitance between multiple touchscreen elements.
For these and other reasons, efficient and effective design of touchscreen display elements is desired.